Volkow is a chocolate lover, you see. She has a special weakness
for dark varieties. Most of the time, she can control her
cravings. But occasionally — usually when she's frustrated or
tired or bored — she gives in. Then she'll overdo it, eating too
much of the stuff.

Sound familiar?

If so, that's because it's a fairly common type of experience.
Most of us can abstain some of the time and give in occasionally,
but more often than not, most of us easily follow the rule of
moderation. But in people who are vulnerable to addiction (via a
mesh of factors including genetics, environment, behavior, and
exposure), this is
where things start to look different, Volkow explains. And
it's at this point where the long-held notion that addiction is
merely a problem of a lack of self-control begins to crumble.

"When you transition from that stage where most of the time you
are able to self-regulate the desires and control and manage your
behavior even though you want to do it, you say it's not a good
idea — when you lose that capacity consistently, that's when you
start to get into the transition of addiction," she says.

A
young man preparing heroin for injection at an apartment in the
Moscow satellite town of Zhukovsky in 2000.Reuters/Dima Korotayev

But, as she continues to explain, the problem is
not simply a behavioral one. It's also influenced by physical
changes that happen in the brain — changes that produce marked
differences between the brains of people who are addicted and
those who are not.

One of those differences, Volkow says, is a dysfunction in areas
of the frontal cortex, a part of the brain that plays a key role
in helping us analyze situations and make decisions. "But if
these areas of the brain are not functioning properly, which is
what repeated drug use [can do] to your brain, it [can erode] the
capacity of frontal cortical areas."

When that happens, your ability to say no to that chocolate bar
gets diminished, or in Volkow's words, "your ability to make
optimal decisions gets dysfunctional."

Volkow's ideas are bolstered by decades of research,
including a 2011
review of studies that she coauthored for the journal Nature.
The authors of a 2004
paper built upon similar research, concluding that addiction
is a learned behavior linked with fundamental changes to the
brains of addicts.

For this reason, it's not as simple as just choosing to use drugs
— or, in Volkow's example, overdo it on the chocolate. And the
more we know about the neurological basis of addiction, the
better we will be able to treat it.